Auto merge of #35667 - ollie27:rustdoc_opaque_structs, r=steveklabnik

rustdoc: Don't add extra newlines for fully opaque structs

Changes the definition for braced structs with only private or hidden fields to save space on the page.

Before:
```
pub struct Vec<T> {
    // some fields omitted
}
```
After:
```
pub struct Vec<T> { /* fields omitted */ }
```

This also cleans up empty braced structs.

Before:
```
pub struct Foo {
}
```
After:
```
pub struct Foo {}
```

[before](https://doc.rust-lang.org/nightly/std/vec/struct.Vec.html) [after](https://ollie27.github.io/rust_doc_test/std/vec/struct.Vec.html)

cc #34713

0 files changed, 0 insertions, 0 deletions